A small pool of corporations is hoarding increasing amounts of unspent cash in its coffers, a factor that economists say could slow down the global economic recovery.

According to a new study by Deloitte, reported on by the Financial Times, approximately one third of the world’s largest non-financial companies on the S&P Global 1200 index is stockpiling most — 82 percent — of the $2.8 trillion in the index’s non-financial corporations’ cash holdings. Those companies are hoarding equity at the highest levels seen since at least 2000.

Non-financial companies include corporations like Apple (which has about $150 billion in cash reserves), Google and Exxon Mobil.

Economists fear that underinvestment in assets that could stimulate growth could slow the economic recovery. Companies have held increasing amounts of cash since the financial crisis, and a record 67 percent of fund managers polled by the Bank of America Merrill Lynch said they were “underinvesting” their assets.